1. Technical Field
The present invention relates to a compact electrostatic relay (electrostatic micro-relay), specifically to a structure of a secondary spring that elastically restores a movable portion in an electrostatic relay.
2. Related Art
In the electrostatic relay, when a moving contact is brought into contact with a fixed contact, an electrostatic actuator is driven to displace the moving contact. When the moving contact and the fixed contact are separated from each other, the moving contact is separated from the fixed contact by an elastic restoring force of a movable spring that is elastically deformed in driving the electrostatic actuator.
In driving the electrostatic actuator, a DC voltage is applied between a movable electrode and a fixed electrode, and the movable electrode is attracted to the fixed electrode by an electrostatic force that acts between the electrodes, thereby displacing a member in which the movable electrode is provided. However, in the electrostatic actuator, due to electrostatic induction or induction polarization generated between the electrodes, occasionally the movable electrode is attracted to and not separated from fixed electrode even if the DC voltage applied between the movable electrode and the fixed electrode is turned off. Further, occasionally the moving contact and the fixed contact are not separated by an adhesive force that is generated when the fixed contact and the moving contact come into contact with each other. Therefore, when the movable electrode is attracted to the fixed electrode, or when the moving contact is in contact with the fixed contact, it is necessary to increase a spring modulus of the movable spring.
For example, Japanese Unexamined Patent Publication No. 6-203726 discloses a contact switchgear in which the spring modulus of the movable spring is increased when the moving contact comes into contact with the fixed contact. FIG. 1A is a perspective view showing a structure of the contact switchgear disclosed in Japanese Unexamined Patent Publication No. 6-203726. In the contact switchgear of FIG. 1A, a base end portion of a movable spring 13 is fixed in a cantilever manner to a moving contact terminal 12 that is vertically provided in an upper surface of a base 11. A moving contact 14 is fixed to a leading end portion of the movable spring 13 that extends in parallel with the upper surface of the base 11. A fixed contact 16 is fixed opposite the moving contact 14 in an upper end portion of a fixed contact plate 15 that is vertically provided in the upper surface of the base 11. An operation controlling member 17 bent into an L-shape is attached to the upper end portion of the fixed contact plate 15, and a leading end 17a of the operation controlling member 17 is opposite the leading end portion of the movable spring 13.
When a rear surface of the movable spring 13 is pressed by a driving member 18, the movable spring 13 is elastically curved, and the leading end portion of the movable spring 13 abuts on the leading end 17a of the operation controlling member 17. When the movable spring 13 is further pressed by the driving member 18, the moving contact 14 is pressed on the fixed contact 16 to close between the moving contact 14 and the fixed contact 16. In the contact switchgear disclosed in Japanese Unexamined Patent Publication No. 6-203726, the movable spring 13 abuts on the operation controlling member 17 before the moving contact and the fixed contact come into contact with each other, thereby achieving shock relaxation of the contact and reduced contact bounce time.
In the contact switchgear disclosed in Japanese Unexamined Patent Publication No. 6-203726, when the moving contact 14 is brought into contact with the fixed contact 16, the movable spring 13 abuts on the leading end 17a of the operation controlling member 17 to increase the spring modulus of the movable spring 13. However, in the contact switchgear disclosed in Japanese Unexamined Patent Publication No. 6-203726, because a driving force of the driving member 18 is the electromagnetic force, the spring modulus of the movable spring 13 is not increased in order to separate the movable electrode and fixed electrode of the electrostatic actuator. Additionally, in the contact switchgear, while the moving contact 14 is in contact with the fixed contact 16, the movable spring 13 is separated from the leading end 17a of the operation controlling member 17 as shown in FIG. 1B, and the spring modulus of the movable spring 13 is returned to the original spring modulus.
Japanese Unexamined Patent Publication No. 2000-164104 discloses an electrostatic micro-relay, in which a movable substrate having a spring property is overlapped on a substrate in which a fixed contact and a fixed electrode are provided, and a moving contact that is opposite the fixed contact and a movable electrode that is opposite the fixed electrode are provided in a lower surface of the movable substrate. In the electrostatic micro-relay, a projection portion is provided in at least one of the movable electrode and the fixed electrode, the projection portion is brought into contact with the other of the movable electrode and the fixed electrode before the moving contact and the fixed contact abut on each other, and the opening force is increased by an elastic deformation partially generated in the movable spring near the projection portion.
In the electrostatic relay, although the original spring modulus of the movable spring can arbitrarily be increased by a position or a height of the projection portion, there is a restriction to the position or the height, which results in a problem in that a degree of freedom of design is degraded by processing preciseness or troublesome design.